J/A+A/564/A125ivo://CDS.VizieR/J/A+A/564/A125doi:10.26093/cds/vizier.35640125CDSBuchner J.Georgakakis A.Nandra K.Hsu L.Rangel C.Brightman M.,Merloni A.Salvato M.Donley J.Kocevski D.2014-10-10T15:29:24Z2014-04-17T09:03:42ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frx-ray-sourcesactive-galactic-nucleiredshiftedActive Galactic Nuclei are known to have complex X-ray spectra that depend on both the properties of the accreting supermassive black hole (e.g. mass, accretion rate) and the distribution of obscuring material in its vicinity (i.e. the "torus"). Often however, simple and even unphysical models are adopted to represent the X-ray spectra of AGN, which do not capture the complexity and diversity of the observations. In the case of blank field surveys in particular, this should have an impact on e.g. the determination of the AGN luminosity function, the inferred accretion history of the Universe and also on our understanding of the relation between AGN and their host galaxies. We develop a Bayesian framework for model comparison and parameter estimation of X-ray spectra. We take into account uncertainties associated with both the Poisson nature of X-ray data and the determination of source redshift using photometric methods. We also demonstrate how Bayesian model comparison can be used to select among ten different physically motivated X-ray spectral models the one that provides a better representation of the observations. This methodology is applied to X-ray AGN in the 4 Ms Chandra Deep Field South. For the ~350 AGN in that field, our analysis identifies four components needed to represent the diversity of the observed X-ray spectra: (1) an intrinsic power law, (2) a cold obscurer which reprocesses the radiation due to photo-electric absorption, Compton scattering and Fe-K fluorescence, (3) an unabsorbed power law associated with Thomson scattering off ionised clouds, and (4) Compton reflection, most noticeable from a stronger-than-expected Fe-K line. Simpler models, such as a photo-electrically absorbed power law with a Thomson scattering component, are ruled out with decisive evidence (B>100). We also find that ignoring the Thomson scattering component results in underestimation of the inferred column density, N_H_, of the obscurer. Regarding the geometry of the obscurer, there is strong evidence against both a completely closed (e.g. sphere), or entirely open (e.g. blob of material along the line of sight), toroidal geometry in favour of an intermediate case. Despite the use of low-count spectra, our methodology is able to draw strong inferences on the geometry of the torus. Simpler models are ruled out in favour of a geometrically extended structure with significant Compton scattering. We confirm the presence of a soft component, possibly associated with Thomson scattering off ionised clouds in the opening angle of the torus. The additional Compton reflection required by data over that predicted by toroidal geometry models, may be a sign of a density gradient in the torus or reflection off the accretion disk. Finally, we release a catalogue of AGN in the CDFS with estimated parameters such as the accretion luminosity in the 2-10keV band and the column density, N_H_, of the obscurer.2014A&A...564A.125Bhttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/564/A125CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/253 : Chandra Deep Field South: multi-colour data (Wolf+, 2008)J/ApJS/155/73 : Photometric redshifts of X-ray sources in CDF-S (Zheng+, 2004)J/A+A/451/457 : X-ray properties of AGN in CDFS (Tozzi+, 2006)J/ApJ/640/167 : AGNs and ULIRGs in the CDF-South (Alonso-Herrero+, 2006)J/A+A/488/73 : Variability-selected AGN in Chandra DFS (Trevese+, 2008)J/AJ/135/1505 : CDFs AGNs X-ray power-law photon index (Saez+, 2008)J/ApJ/680/130 : Mid-IR colors of AGNs in the MUSYC ECDF-S (Cardamone+, 2008)J/A+A/497/81 : Variability-selected AGN in CDFS (Boutsia+, 2009)J/ApJ/693/1713 : Spectroscopy of X-ray sources in ECDF-S (Treister+, 2009)J/ApJS/187/560 : Photometric redshifts of the 2Ms CDF-S (Luo+, 2010)J/ApJS/195/10 : The CDF-S survey: 4Ms source catalogs (Xue+, 2011)J/A+A/555/A42 : The XMM-CDFS catalogues (Ranalli+, 2013)https://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/564/A125https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/564/A125http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/564/A125https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/564/A125https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/564/A125http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/564/A125GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/564/A125/catalog (Catalog of the derived quantities for each source in the Chandra Deep Field South (CDFS))https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/564/A125/catalog?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/564/A125/catalog?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/564/A125/catalog?GETtext/xml+votable180.050000true53.12575-28.0059080.0055555555555555566/35935 35957https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/564/A125?format=asciiX-rayOpticaldefaultJ/A+A/564/A125/catalogCatalog of the derived quantities for each source in the Chandra Deep Field South (CDFS)XID[1/570] Source identificationmeta.id;meta.mainintprimaryRAJ2000Hour of Right Ascension (J2000)pos.eq.ra;meta.mainDEJ2000Degree of Declination (J2000)pos.eq.dec;meta.mainCt[27/32100] Full-band (0.5-8ke) photon countsctphot.count;em.X-rayintz[0.1/5.4] Redshift (z, median)src.redshiftfloate_z? z lower 1-{sigma} equivalent quantilestat.error;src.redshiftfloatnullableE_z? z upper 1-{sigma} equivalent quantilestat.error;stat.maxfloatnullablelogLXLogarithm of intrinsic luminosity (erg/s) in the 1-9 keV restframe band (L, median)log(1e-07W)phys.luminosity;em.X-rayfloate_logLXlogLX lower 1-{sigma} equivalent quantilelog(1e-07W)stat.errorfloatE_logLXlogLX upper 1-{sigma} equivalent quantilelog(1e-07W)stat.error;stat.maxfloatlogNHLogarithm of neutral hydrogen equivalent column density (N_H_, median)log(cm**-2)phys.columnDensityfloate_logNHlogNH lower 1-{sigma} equivalent quantilelog(cm**-2)stat.errorfloatE_logNHlogNH upper 1-{sigma} equivalent quantilelog(cm**-2)stat.error;stat.maxfloatGammaIntrinsic photon index ({Gamma}, median)meta.code;spect.indexfloate_GammaGamma lower 1-{sigma} equivalent quantilestat.errorfloatE_GammaGamma upper 1-{sigma} equivalent quantilestat.error;stat.maxfloatfscat[0/10] Scattering fraction (f_scat_)%stat.fit.paramfloate_fscatfscat lower 1-{sigma} equivalent quantile%stat.errorfloatE_fscatfscat upper 1-{sigma} equivalent quantile%stat.error;stat.maxfloatR[0/6] Reflection component, relative normalisation (R, median)stat.fit.paramfloate_RR lower 1-{sigma} equivalent quantilestat.errorfloatE_RR upper 1-{sigma} equivalent quantilestat.error;stat.maxfloatKLNHInformation gain for column density parameter (KL) in ban unitsstat.fit.paramfloatNotesNotes (1)meta.notechar